The invention relates to a direct electrodynamic linear drive comprising a drive coil system made up of a plurality of adjacently arranged coils, said system being adapted to be operated by a switched exciting voltage, and a plurality of adjacently arranged permanent magnets, means being provided for relatively moving on the one hand permanent magnets and the drive coil system on the other hand.
In the case of a previously proposed linear direct drive disclosed in the German patent publication 19,748,647 A1 the coils are arranged on the inner side of a ferromagnetic tube, whereas the permanent magnets are able to be moved within the drive coil system. It is more especially in the case of elongated arrangements that this leads to substantial bearing problems for the permanent magnets able to be moved within the coils and a force transmitting element must be fixed to the magnets.
One object of the invention is to create an electrodynamic linear drive, in the case of which the armature may be simply and reliably supported by bearing means even in the case of an extremely long drive.
This object is to be attained with a direct electrodynamic linear drive comprising a drive coil system composed of coils arranged in a row alongside each other on an elongated ferromagnetic core, which coil system is able to be supplied with a switched exciting voltage, and a ferromagnetic tube fitting around the drive coil system, a plurality of permanent magnets being arranged on the inner side of the said tube in a row alongside each other in the longitudinal direction of the tube, the core being provided with drive coil system and designed as a stator and the tube provided with the permanent magnets being designed as an armature.
The ferromagnetic tube surrounding and holding the drive coil system has a multiple function and serves on the one hand as guide element for the armature and on the other hand as a magnetic return member for containing the magnetic field. Such a ferromagnetic tube can be reliably and exactly guided on the outer side by longitudinal guide bearings readily for longitudinal movement, whereas the drive coil system may be fixed in the interior of the tube or, respectively, of the permanent magnets in a stationary manner.
The measures recited in the claims represent advantageous further developments and improvements of the novel direct linear drive specified.
It is an advantage for the tube to be slidingly mounted in a longitudinal duct in a housing, the drive coil system extending into the longitudinal duct from one side. This means that a direct linear drive can be manufactured with an extremely small housing cross section and a great longitudinal extent.
In order to ensure that the drive coil systems is centered in the ferromagnetic tube with relatively small distances from the permanent magnets a non-ferromagnetic guide tube extends along radial inner faces of the permanent magnets, at least one support element being arranged additionally on the elongated core for sliding or rolling along the inner face of the guide tube.
The radially magnetized permanent magnets fit about the drive coil system and are more particularly made up of radially or diametrally magnetized magnet segments or magnet shells.
The guide tube and the permanent magnets may possess a round, oval-like or prismatic cross section, all non-round cross sections preventing relative rotation.
A particularly compact and readily handled arrangement is one in which the housing has integrated in it an electronic regulating and/or control system and/or power system for electrically supplying the drive coil system and/or an electrically operated detecting means for the armature.
The cylindrically wound drive coil system can have one or more strands, and in the case of several coil strands they will be placed on the core in sequence with axially alternating directions of winding. The width of a coil will in this case be equal to the width of a permanent magnet divided by the number of coil strands.
In the case of a multi-strand drive coil system it is convenient to provide for electronic or mechanical commutation of the coil strands in accordance with their respective position in relation to the permanent magnets of the armature.
In order to find or ascertain the armature position a displacement measuring system is provided in the housing, the drive coil system preferably being designed as a displacement or path measuring system.
In the case of a preferred design of such an integrated displacement measuring system the drive coil system is placed in circuit as a differential choke system, wherein by having regions with different magnetic saturation in the iron of the core, caused by the magnets of the armature, changes in inductance are caused and owing to the motion of the armature are correspondingly shifted out of position, a detecting and evaluating means being provided responsive to the inductance changes in the inductance fractions of the differential choke system and therefrom finding the position. Such an integrated displacement or travel measuring system is of independent significance as a subcombination and may also be employed in other direct linear drives, in the case of which a permanent magnet arrangement is able to be shifted in relation to the drive coil system and the latter comprises coils in a row on a ferromagnetic core.
Further advantageous developments and convenient forms of the invention will be understood from the following detailed descriptive disclosure of embodiments thereof in conjunction with the accompanying drawings.